In various electric/electronic devices, a switch activated by a mechanical switching operation is used to control, for example, switching of ON-OFF of a power supply and/or switching of electric circuits. It is known that such switch includes, for example, a slide switch, a toggle switch, a rotary switch, a push switch, a rocker switch (or a tumbler switch) and so on.
Conventionally, such switch is generally used in combination with a current fuse in order to improve safety of the electric/electronic device by protecting a load of the electric circuit from overcurrent (hereinafter such switch without a function of protection is referred to as the conventional general switch). For example, in an electric circuit of electric toys, home electric appliances or the like, the current fuse is used while being inserted between the switch and the load in series.
In recent years, a Positive Temperature Coefficient (PTC) element is used as an overcurrent protection element in place of the current fuse, and a switch using a PTC element is proposed (see, for example, Japanese Patent Publication No. JP-A-1998-188716. In this type of switch, the PTC element is located within an operating part so that the PTC element is serially connected with the load. More specifically, as to a rotary switch, the PTC element is incorporated in the operating part by embedding a PTC material (PTC resin) in the operating part rotatable in a certain plane and forming a polar plate on an exposed surface of the PTC material (see FIG. 3 in Patent Literature 1). According to this switch construction, there is provided the switch having a function of overcurrent protection, which is not necessarily used in combination with a current fuse.
The term “PTC material” in the present description means a material having a Positive Temperature Coefficient as is known in the field of the electric/electronic circuit technology. The PTC material has its electric resistance (or an impedance) at a relatively low level under a relatively low temperature condition (e.g. an ordinary or room temperature), but shows shew a steep increase in the electric resistance on exceeding a certain temperature (hereinafter referred to as a trip temperature). Throughout the present description, the former state of the PTC material is called “Low state,” and the latter state thereof, “High state.” Then, the “PTC element” means an element constructed by forming conductive members on a surface of the PTC material at a distance from each other. The conductive members function as electrodes, and are also simply referred to as electrodes or polar plates.